U.S. patent application number 13/702303 was filed with the patent office on 2013-11-07 for optical antennas with enhanced fields and electron emission.
The applicant listed for this patent is Maha Achour, Ezekiel Kruglick, Phillip J. Layton. Invention is credited to Maha Achour, Ezekiel Kruglick, Phillip J. Layton.
Application Number | 20130294729 13/702303 |
Document ID | / |
Family ID | 45098651 |
Filed Date | 2013-11-07 |
United States Patent
Application |
20130294729 |
Kind Code |
A1 |
Layton; Phillip J. ; et
al. |
November 7, 2013 |
OPTICAL ANTENNAS WITH ENHANCED FIELDS AND ELECTRON EMISSION
Abstract
An electromagnetic energy collecting and sensing device is
described. The device uses enhanced fields to emit electrons for
energy collection. The device is configured to collect energy from
visible light, infrared radiation and ultraviolet electromagnetic
radiation. The device includes a waveguide with a geometry selected
to enhance the electric field along a conductor to create a high,
localized electric field, which causes electron emission across a
gap to an electron return plane.
Inventors: |
Layton; Phillip J.; (San
Diego, CA) ; Kruglick; Ezekiel; (Poway, CA) ;
Achour; Maha; (Encinitas, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Layton; Phillip J.
Kruglick; Ezekiel
Achour; Maha |
San Diego
Poway
Encinitas |
CA
CA
CA |
US
US
US |
|
|
Family ID: |
45098651 |
Appl. No.: |
13/702303 |
Filed: |
June 8, 2011 |
PCT Filed: |
June 8, 2011 |
PCT NO: |
PCT/US11/39671 |
371 Date: |
March 12, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61352697 |
Jun 8, 2010 |
|
|
|
Current U.S.
Class: |
385/40 |
Current CPC
Class: |
B82Y 20/00 20130101;
H01L 31/035209 20130101; G02B 6/00 20130101; Y02E 10/52 20130101;
H01L 31/0547 20141201; H01Q 21/064 20130101; G02B 6/1226
20130101 |
Class at
Publication: |
385/40 |
International
Class: |
G02B 6/00 20060101
G02B006/00 |
Claims
1. A field-enhancing energy collection device, comprising: a
substrate comprising a base surface, the base surface comprising a
recessed structure having one or more angled wall surfaces that
taper downward away from the base surface, between which angled
wall surfaces is formed a recess void, the recess void being empty
or filled with a transparent or translucent material, the one or
more angled wall surfaces coming in contact or close proximity to
one another at a distance from the base surface, the one or more
angled surfaces comprising an electromagnetic energy conducting
waveguide optically exposed to the recess void; and an electrode
adjacent or in close proximity to the substrate, wherein the
field-enhancing energy collection device comprises a field
enhancement region separated from the electrode.
2. The field-enhancing energy collection device of claim 1, wherein
a curvature of the recess void changes at said distance from the
base surface.
3. The field-enhancing energy collection device of claim 1, wherein
the device comprises a gap between the electrode and the
electromagnetic energy conducting waveguide of the recessed
structure.
4. The field-enhancing energy collection device of claim 3, wherein
the gap between the electrode and the electromagnetic energy
conducting waveguide comprises a vacuum void, a gas, a substrate or
a combination thereof.
5. The field-enhancing energy collection device of claim 3, wherein
the gap comprises a photovoltaic material.
6. The field-enhancing energy collection device of claim 5, wherein
the photovoltaic material comprises an electrolyte and TiO.sub.x,
wherein `x` is a number greater than zero.
7. (canceled)
8. The field-enhancing energy collection device of claim 1, wherein
the electromagnetic energy conducting waveguide includes a cathode
and the electrode includes an anode.
9. (canceled)
10. The field-enhancing energy collection device of claim 8,
wherein the substrate comprises an insulating or semiconducting
material, and wherein the cathode includes one or more materials
selected from the group consisting of Al, Ag, Au, Cu, Pt, Ni, Mn,
Mg, Ru, Rh, C, W or graphene.
11. (canceled)
12. The field-enhancing energy collection device of claim 1,
wherein the base surface dimensions of said recessed structure is
greater than 500 nanometers ("nm").
13. (canceled)
14. The field-enhancing energy collection device of claim 1,
wherein the substrate is electrically insulated from the
electromagnetic energy conducting waveguide.
15. The field-enhancing energy collection device of claim 1,
wherein the recessed structure is in a conical, half dome,
pyramidal, polygonal, linear track, or circular track
configuration.
16. (canceled)
17. (canceled)
18. The field-enhancing energy collection device of claim 1,
further comprising a transparent overcoat protection layer adjacent
to the base surface.
19. The field-enhancing energy collection device of claim 1,
wherein the electromagnetic energy collection is situated on a
surface of the recessed structure.
20. The field-enhancing energy collection device of claim 1,
wherein the substrate comprises more than one recessed structure
comprised in an array of recessed structures.
21. The field-enhancing energy collection device of claim 20,
wherein each recessed structure in the array of recessed structures
includes a cathode that is spaced apart from an isolated anode.
22. The field-enhancing energy collection device of claim 21,
wherein each recessed structure includes an electromagnetic energy
conducting waveguide that is in electrical communication with the
electromagnetic energy conducting waveguide of the recessed
structure.
23.-29. (canceled)
30. The field-enhancing energy collection device of claim 1,
wherein the field enhancing region is defined by the one or more
angled wall surfaces.
31. The field-enhancing energy collection device of claim 1,
wherein the field enhancing region has a sharp tip relative to the
rest of the surface.
32.-51. (canceled)
52. An electromagnetic field concentrator, comprising: one or more
waveguides, an individual waveguide of the one or more waveguides
having a substrate comprising one or more angled surfaces that
taper away from a first end of the substrate toward a second end of
the substrate, the one or more angled surfaces defining a recess
void configured to collect electromagnetic radiation, the one or
more angled surfaces formed of an electromagnetic radiation
conducting material; and an electrode adjacent to the one or more
waveguides, the electrode configured to collect electrons generated
upon the application of electromagnetic radiation to the one or
more waveguides, wherein the electrode and the second end define a
gap between the waveguide and the individual waveguide of the one
or more waveguides, and wherein the electromagnetic field
concentrator comprises a field enhancement structure adjacent to
the electrode.
53. The electromagnetic field concentrator of claim 52, wherein a
curvature of the recess void changes toward the second end.
54. The electromagnetic field concentrator of claim 52, wherein the
first end has a first width and the second end has a second width,
the first width being greater than the second width.
55. The electromagnetic field concentrator of claim 52, wherein the
electrode is the anode of the electromagnetic field
concentrator.
56. A field-enhancing energy collection device, comprising: a
support structure comprising at least one recessed structure having
a first end and a second end opposite from the first end, the
recessed structure having one or more angled wall surfaces that
taper downward away from the first end, the angled wall surfaces
defining a recess void, the recess void being empty or filled with
an optically transparent or translucent material, the one or more
angled wall surfaces coming into contact with or close proximity to
one another at or near the second end, the one or more angled
surfaces comprising an electromagnetic energy conducting waveguide
optically exposed to the recess void; and an electrode adjacent to
the support structure, the electrode configured to collect
electrons generated upon the application of electromagnetic
radiation to the at least one recessed structure, the electrode
spaced apart from the electromagnetic energy conducting waveguide,
wherein field-enhancing energy collection device comprises a field
enhancement structure adjacent to the electrode.
57. The field-enhancing energy collection device of claim 56,
wherein the second end comprises a field enhancement region.
58. The field-enhancing energy collection device of claim 57,
wherein the field enhancement region comprises a substantially
sharp tip.
59. The field-enhancing energy collection device of claim 56,
wherein a curvature of the recess void changes toward the second
end.
60.-61. (canceled)
62. The field-enhancing energy collection device of claim 56,
wherein the support structure is formed of an optically transparent
material.
63.-68. (canceled)
Description
CROSS-REFERENCE
[0001] This application claims priority to U.S. Provisional Patent
Application Ser. No. 61/352,697, filed on Jun. 8, 2010, which is
entirely incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] Traditionally, ultraviolet (UV), visible and infrared
electromagnetic or light energy is collected using semiconductors
with bandgap energies tuned to the desired photon energy to be
collected. Alternatively, light energy may be converted into
thermal energy by an absorber and then the heat energy may be
collected by traditional thermal energy collectors, such as
sterling engines, steam engines or other methods. These major solar
energy collection technologies may be further grouped as follows:
1) inorganic, semiconductor based photovoltaic ("PV") generation,
2) organic based PV generation, 3) nanotechnology, which includes
carbon nanotubes and quantum dots, and 4) solar thermal or solar
concentrator technologies. Silicon (semiconductor-based) PV
technologies, solar thermal technologies and solar concentrator
technologies are the most widely used currently commercially
available and mature technologies.
[0003] In some cases, photovoltaic technologies use discrete
bandgap potentials generated by p-doped and n-doped semiconductor
material to collect energy from light. Typical inorganic PV
efficiencies may range from 10% for the single junction cells up to
around 28% for triple junction PV cells. PV technology is limited
physically to less than 33% energy collection efficiency by bandgap
energy collection limitations and by semiconductor electrical
resistance.
[0004] Additionally semiconductor-based PV has high costs
associated with the materials used and the manufacturing process.
The material costs include the high cost to produce pure wafers and
the use of rare and expensive materials. The manufacturing costs
include the huge capital cost to build a semiconductor facility,
the control of toxic materials used and the cleanliness requirement
to prevent any impurities from doping the product while under
manufacture. These costs may be reasonable for integrated circuit
(IC) electronics because most, if not all features required to
permit the IC to function may be located in a small area, with many
devices being produced on a single wafer.
[0005] In contrast to the needs for IC electronics, solar
collection technology requires large surface areas to collect
light. The large area requirement provides an inherent limitation
to devices that use expensive processes because of the surface area
cost to generate PV-based solar energy. Therefore, there are cost
restrictions for the use of inorganic PVs for many energy
markets.
[0006] Another major downside for current PV technology is the use
of toxic materials during processing of PV devices and in the final
PV product. After the end of life of current PV devices, the
environmentally toxic or hazardous materials contained in such
devices creates an environmental disposal problem.
[0007] Another category of technology that may be used to collect
photon energy includes sensors that use voltage enhanced field
emission. Such devices use high voltages to detect typically
low-intensity photons using the photoelectric effect. Such devices
have a net energy loss and amplify a signal using an external power
source. These devices consume more power than they produce and are
not useful as energy collectors.
[0008] Another category of technology is based on a recent finding
that electric field enhancement on existing detectors may improve
the performance of photo-detectors. This method of enhancement uses
surface structures to enhance the electric field in desired
locations. The enhanced electric fields created in accordance with
this category of technology allow greater electron mobility in
devices.
[0009] Although conventional antennas convert electrical current
from (to) antenna structures to (from) far-field, optical antennas
may also be used for near-field applications such as imaging and
touchscreen displays by contact sensors. Antenna structures may be
designed using rigid or flexible substrate, metallic, and
dielectric layers to give more integration flexibility and enable
electromagnetic field manipulation through leveraging the
geometrical shape of the optical antenna arrays at the macro-scale.
Such combination of micro-geometrical structure at the unit cell
level and macro-geometrical feature at the array level provide more
degrees of freedom in defining the virtual values of the effective
permittivity and permeability of the array. For instance, using
inner layers of metamaterial structures with dispersive properties
within the light spectrum to improve the optical antenna
efficiencies and enable manipulation of the electromagnetic
absorption and refraction at the air and inner interfaces.
Furthermore, optical antennas may perform such conversion with and
without 1) thermal conversion, 2) using plasmon frequencies of
metal, or 3) leveraging quantum properties of material used to
build such structures.
[0010] As promising as these new technologies are, most are
restricted to collecting light using discrete quantum energy bands,
which imposes the same inherent efficiency limitations as
semiconductor PV technologies. Increasing the number of junctions
or wells increases the number of bandgaps and increases the useable
energy, which results in increased efficiency across the visible
light spectrum. As with inorganic semiconductors, this approach has
a downside because each new well or junction creates a layer that
may interfere with (mask) the well or junction below it and
increase the path length of both the light and the free charge,
which increases the losses from absorption and electrical
resistance. Furthermore, nanotechnology and quantum dots still have
issues with toxicity, with the ability to manufacture and with
efficiency.
[0011] The underlying structures of these optical antennas may be
manufactured more economically and with high-yield allowing these
small and simple structures to be used in various applications
where size, cost, efficiency or precision is relevant.
SUMMARY OF THE INVENTION
[0012] Systems and methods disclosed herein are related to optical
antennas that produce energy from incident electromagnetic waves
using a field concentrating method to create an electron emission
from a distressed field source. Such optical antennas are based on
nanostructures formed using conductive and dielectric layers to
capture light and convert it to energy using either current or
voltage, or emit light from applied current (voltage) or highly
distressed electromagnetic fields.
[0013] In some embodiments, the electromagnetic (EM) fields of
light are locally enhanced by physical features of a photon
collector and conversion design. In an embodiment, using the
electromagnetic wave nature of light, the electric and the magnetic
fields of the light wave are enhanced using structural geometries
and layering between conductor and insulator or dielectric layers.
In another embodiment, metal-coated nanospherical particles create
collective coupling of electrons to an incident electromagnetic
wave. In some cases, the size of the particle and the metal
determine the characteristics of this coupling, which is also
called a plasmon wave. In another embodiment, plasmon waves create
a strong local field enhancement.
[0014] In some embodiments, field enhancement is created using a
waveguide with optical antenna functionalities with and without
leveraging plasmons. Incident light is trapped in the structures in
the form of waveguides resonating over a broad range of frequency
range, enabling more light to be captured and converted to
electrical current through the high concentration of fields on part
of the structure, hence improving overall efficiency. Plasmons
occur at the interface of a metal and a dielectric. Under the right
circumstances, light waves induces resonant interactions between
the waves and the mobile electrons at the surface of the metal.
Depending on the optical antenna structure, these resonances span a
broad range of frequency ranges associated with the nature of
waveguides trapped in the structure or through excitation of higher
order modes. The interactions generate surface plasmons. Therefore
using selective geometries on the surface metals induces frequency
dependent resonant absorption.
[0015] System and methods described in some embodiments improve the
collection efficiency of electromagnetic radiation in general and
more specifically the collection efficiency of visible light. In
some instances, this effect if achieved by 1) removing the quantum
bandgap restrictions and utilizing a spectrum of electromagnetic
radiation (e.g., for visible wavelengths, utilizing the entire
visible and near visible spectrum, and/or 2) lowering the
resistance of free electrons by improving the matching between the
antenna structure and adjacent elements responsible for collecting
the induced electrical current. There is a direct connection
between the distressed field, field concentrate, and enhanced
fields with conventional antenna parameter such as matching,
radiation fields, directivity, efficiency, and so forth.
Additionally, in certain instances, the systems and methods
described herein do not require or do not comprise semiconductor
materials. In some instances, the absence of semiconductor
materials results in devices that are significantly less expensive
than traditional semiconductor-based photovoltaics. In some
potential applications, semiconductor is the preferable choice.
[0016] In some embodiments, systems and methods described herein
collect electromagnetic energy using enhanced fields to create
electron emission. In some cases, systems and methods described
herein use feature sizes on the scale of the incident
electromagnetic wave to generate localized field enhancements in
conductors to capture the energy from the electromagnetic spectrum.
In other words, the feature sizes, structural features, material
used, and/or geometries (e.g., widths, lengths, diameters, shapes,
depths, descending angles, or the like of a recessed structure; the
distances between recessed structures; shapes or connectivity of
anodes; or the like) of a system or method described herein are
adjustable in order to improve overall energy collection, tune a
system to improve the manner and efficiency in which energy is
collected from a certain wavelength of light, and matching to
enable efficient conversion to electrical current, or the like.
[0017] In some embodiments, the electric field is captured in a
conductor with the geometry of the device creating a region of high
field strength. The strength of the field is sufficient to cause
electron emission across a gap to a ground plane or through an
interface to the electrical current ports, creating a potential
difference and a current. In some embodiments, a system or method
described herein is utilized to collect UV, visible and/or infrared
light. For example, the specific feature sizes and geometries
provide a system wherein the entire spectrum of ultraviolet (UV),
visible, and/or infrared (IR) light is captured using a single
geometry.
[0018] System and methods provided herein are applicable in various
settings, including, for example, solar energy collection, sensors,
near-field imaging, touch-screen, cloaking, concentrated
electromagnetic energy collection and optical to electrical signal
conversion. As another example, systems and methods provided herein
are used for applications that require electric power or for other
electromagnetic sensor and system applications.
[0019] In an aspect, a field-enhancing energy collection device or
system comprises: [0020] a substrate, [0021] the substrate
comprising a base surface, [0022] the base surface comprising at
least one recessed structure having one or more angled wall
surfaces that taper downward away from the base surface, between
which angled wall surfaces is formed a recess void, [0023] the
recess void being empty or filled with a transparent or translucent
material, [0024] the one or more angled wall surfaces coming into
contact or close proximity at a distance from the base surface,
[0025] the one or more angled surfaces comprising an
electromagnetic energy conducting waveguide material, [0026] the
electromagnetic energy conducting waveguide material being in
optically exposed to the recess void, and [0027] an anode, wherein
the device comprises a gap between the anode and the
electromagnetic energy conducting waveguide material of the
recessed structure.
[0028] In some embodiments, the electromagnetic collecting region
of the device comprises an array of optical antenna structures and
waveguides (e.g., within a recessed structure) across a plane
(e.g., a base surface). In certain embodiments, the recessed
structure(s), optical antenna structures, waveguides, anodes, or
other portions of a system or device described herein are tailored
to the electromagnetic spectrum to be collected. Preferably, the
recessed structure comprises, and the waveguide is present on the
surface of or optically exposed to the surface of (i.e., light may
reach it), one or more sloping or tapered structures, such as
conical structures, pyramidal or other polygon structured that is
angled or tapered. Such optical antennas are similar to
radiofrequency ("RF") horn antennas with the exception that they
operating at light frequencies where conductors and insulators
potentially behave differently. In some embodiments, the angle
between the base surface and the interior wall surface of the
recessed structure (see .THETA. in FIG. 3A) is about 90.degree., or
between about 70.degree. and 85.degree., or between about
54.degree. and 70.degree., or less than 90.degree., or the like. In
some instances, the size of the top down to the bottom (depth) of
the recessed determines or influences (at least in part) the
wavelengths of light that will be collected. In some instances, the
top surface further incorporates curved or slanted edges to further
improve the trapping of light in the structure. In some instances,
the bottom surface further incorporates curved or slanted edges to
further improve the field intensity at the electron emission level
and matching condition with the electrical circuit interface. In
some instances, these structures provide for or facilitate the
collection of a spectrum of electromagnetic energy collection.
Generally, these structures form the cathode or electron emitter
for systems and devices described herein.
[0029] Additionally, in some instances, the spacing between two or
more of these structures (providing for a base surface dimension of
at least two recessed structures--see 311 in FIG. 3A) creates
resonance regions for other wavelengths. In other words, in certain
instances the sloping structures collect one spectrum of
wavelengths and the distance between them collect another, thus
providing for or facilitating the collection of multiple
wavelengths. In some cases, the optical antenna structure at the
unit cell level differs from one point to another in the array
enabling higher manipulation of electromagnetic field absorption
and propagation at the air or inner layer interfaces.
[0030] An additional embodiment includes a tube structure (e.g.,
wherein .THETA. is 90.degree.). In some cases, the tube structure
is circular, ellipsoidal or a polygonal in shape. Instead of a
tapered structure, this option has one width or a limited number of
widths for ellipsoidal or polygonal shape. In certain instances,
such a structure provides a device or system that suitable for
collecting energy from specific wavelengths. In certain instances,
an array of such structures (e.g., having a plurality of different
base surface dimensions and/or geometries) with set distances also
provides additional specific wavelengths to be collected. In some
embodiments, such systems are useful as sensors or in energy
collection devices wherein energy from specific types/wavelengths
of light are collected. In certain instances, varying the width of
an array of these devices allows collecting wavelength-specific
information by determining the signal strength from each device
that has a particular size. As such a device such as this is
optionally utilized in a specific frequency detector.
[0031] In certain embodiments, the collecting structure (recessed
structure) is conical with a circular cross section; however, in
other embodiments the collecting structure has other shapes, such
as, for example, a square, ellipsoidal a pentagon, polygon or even
parabolic. In some instances, the tapered cross section of the
collecting structure creates nodes for each wavelength to be
collected at multiple locations along the surface. In some
instances, the collecting structure further incorporates curved,
spiraling or slanted edges to further improve the field intensity
at the electron emission level and matching condition with the
electrical circuit interface. In some instances, a configuration
packs many structures closely together such that a substantial
portion of a collecting surface is covered by cones. In certain
applications, tapered polygon structures such as hexagons are more
advantageous for increasing the packing density. Additional
embodiments include nonuniform regions to change the resonance
areas or to create nodes to enhance particular frequencies over
others.
[0032] In some embodiments the structures are tracks that are
triangular or parabolic. In some instances, the device is
manufactured with concentric or spiraling circles, squares or other
structures. This enables the device to have several isolated
regions that could limit the effects of damage or could also ease
manufacturing the device. In some instances, the embodiments of the
structure into a device are clustered to bypass the ones with bad
cells. In general, the fabrication process provides that no cells
are shorted during manufacturing; however some may present an open
circuit.
[0033] For the preferred broad spectrum energy collection
embodiment, the structures are inverted such that the base of the
structure is at the top and the structure tapers downwardly. The
base at the top faces the source of solar or other light energy. In
some instances, the top base diameter (or other cross-sectional
dimension, i.e., base surface dimension of a recessed structure) is
on the order of the longest wavelength of collected light, which
comprises the infrared (IR) portion, visible portion and the
ultraviolet (UV) portion of the electromagnetic spectrum. For the
visible portion, the waveguide base (or base surface dimensions)
is, in one embodiment, between about 1000 nanometers (nm) and 600
nm, or about 800 nm and 750 nm. The dimensions are shorter for
ultraviolet light. In some embodiments, for infrared collection,
the base is larger or greater than 1 micron. In certain instances,
this increase in size at the base above 1 micron will decrease the
collection efficiency of the visible light since a greater amount
of the area is dedicated to infrared light. As such the desired
range of frequencies to be collected need to be considered when
choosing the waveguide collection dimensions.
[0034] In certain instances, sloping geometry, similar to horn
antennas, creates an environment where a range of wavelengths of
the incident spectrum have a trap region with a respective diameter
or width in the waveguide structure corresponding to each
wavelength of light. In some cases, this trapping is further
enhanced by incorporating slanted or cylindrical surfaces at the
top or bottom surfaces, or by including grooves or some sort of
surface roughness along the inner surface of the sloping geometry,
or by including metamaterial resonating structures or
metal-insulator-metal ("MIM") layer along the inner side.
[0035] In some instances, waveguide structure comprises a conductor
(e.g., an electromagnetic energy conducting material) with a
thickness determined by the desired collection properties. In
certain embodiments, the thickness is on the order of the
wavelength of electromagnetic skin depth in the conducting medium.
In specific embodiments, conductors useable for the walls of the
waveguides include metals such as gold, silver, copper and
aluminum. In other embodiments, other non-metallic materials are
also used. For example, graphene has particular relativistic
quantum electrodynamic properties that create a very low-resistance
light trap. In suitable instances, any material that creates a
plasmon wave at the conducting surface interface will work to
varying degrees depending on the incident wavelength and the
desired collection spectrum. In some embodiments, the conducting
(or waveguide) layer is supported by either a dielectric such as
SiO.sub.2 or some other easily manufactured material such as
plastic or another nonconducting medium.
[0036] In one optional mode, multiple conductors, multiple metal
layers, Metal-Insulator-Metal (MIM) layers, or metamaterial-based
layers are used to modify the plasmon wave generated at the
interface between the different material layers, further enhance
trapping light with MIM layers, or enable electron quantum
tunneling along the MIM layers. In suitable instances, standing
waves in the metal coupled with a plasmon wave at the
dielectric/metal or bimetal interface create the high field region
at the tip of each waveguide structure. The plasmon wave at the
conducting material interfaces creates a waveguide along the cone
for shorter wavelength light that has not yet reached the region of
the cone that matches its wavelength. In certain instances, the
enhanced field at the tip structure of the waveguide structure
creates a localized high field area where electrons are emitted
across a gap. In suitable instances, the gap is tailored to the
device based on the dielectric strength of the gap and the required
operating voltage of the device. In specific embodiments, of a
configuration for visible light, the gap distance is less than the
shortest wavelength of light to be collected, however in some
instances a gap distance greater than this will also work. This
waveguide tip creates a cathode for the field emitter.
[0037] In suitable instances, the enhanced field causes electrons
from the conducting cathode to jump across the gap to the anode or
ground plane when proper matching is reached at the electron
collection interface. In some embodiments, the electron current is
a function of the intensity of light, geometry and materials of the
waveguide, the dielectric material, the distance between the two
conductors, any voltage across the cathode anode gap and the
enhanced field at the point. In certain embodiments, the voltage is
a function of the field strength and the dielectric material or
vacuum gap.
[0038] In suitable instances, a ground plane, or anode collects the
emitted electrons. The ground plane is connected to a load with
appropriate matching conditions. In some embodiments, the load is
advantageously a motor, a battery, a storage device or any other
device that uses or collects the electrical energy generated by the
energy collector disclosed herein or sense current intensity in the
case of sensors or touchscreen applications. In one embodiment the
anode has an inverted tapered structure pointing up towards the
cathode, the cathode being the electron emitting tip of the conical
structure. This creates a higher field disturbance between the
cathode and anode, lowering the required field for emission.
[0039] In certain embodiments of the systems and methods, the
cathode and anode are connected to a voltage source that changes
the field between the cathode and anode. In some embodiments, this
connection increases the voltage or increase the electron current
for various types of application loads. In certain embodiments,
this also causes the anode to emit electrons, reversing the
current. In suitable instances, there are certain applications,
where a current reversal is required after the application of
certain voltages; these applications in some instances include AC
voltage regulation or coupling.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] A system and method in accordance with aspects of the
present invention is disclosed herein in accordance with the
attached drawings in which:
[0041] FIG. 1 illustrates a perspective view of an embodiment of a
tapered waveguide collecting structure wherein light (or energy at
another wavelength of the electromagnetic spectrum) enters from the
top into the waveguide, which is the base of the inverted tapered
structure, in accordance with an embodiment of the invention;
[0042] FIG. 2 illustrates a perspective view of an array of
waveguides or cathodes over an anode, in accordance with an
embodiment of the invention;
[0043] FIGS. 3A and 3B illustrate cross-sectional elevational views
of the array of waveguide, structures along which cathodes will be
located, of FIG. 2 and show a dielectric between the cathodes and a
conducting ground plane (anode), in accordance with an embodiment
of the invention;
[0044] FIG. 4 illustrates the enhancement of the electric field at
the tip of a collecting cone, in accordance with an embodiment of
the invention;
[0045] FIGS. 5A and 5B show tapered waveguide structures with an
inverted anode pointing to each cathode, to increase the localized
field enhancement, in accordance with an embodiment of the
invention;
[0046] FIG. 6 illustrates an electrical circuit for a variation of
system that uses a low current or zero current voltage source to
increase the voltage across the gap between the ground plane and
electron emitting tip of the collecting structure, in accordance
with an embodiment of the invention;
[0047] FIG. 7 shows a specialized structure where the waveguide
structure is designed to collect a more narrow spectrum of
wavelengths of light, this structure is not tapered and is a
cylinder, in accordance with an embodiment of the invention;
[0048] FIG. 8 shows a track structure were each cathode is a
continuous region. The emission region is formed by the tapered
lower region of the device, in accordance with an embodiment of the
invention;
[0049] FIG. 9 shows a functional block diagram of optical antennas,
in accordance with an embodiment of the invention;
[0050] FIG. 10 schematically illustrates embedding optical antenna
nano-structures into macro geometries, in accordance with an
embodiment of the invention;
[0051] FIG. 11 illustrates variations of tapered structures, in
accordance with an embodiment of the invention; and
[0052] FIG. 12A illustrates an optical waveguide having a field
enhancement region, in accordance with an embodiment of the
invention. FIG. 12B illustrates an optical waveguide having a field
enhancement region, in accordance with an embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0053] The drawings and the following description illustrate
preferred embodiments of a system and method for implementing the
present invention. In some embodiments, other shapes and
configurations are also used to create the disclosed effect of
collecting the electric field from the electromagnetic wave and
funneling the electric field to a localized field region above a
conducting plane where electrons are emitted from the distress
field point or line.
[0054] The term "waveguide," as used herein, refers to a structure
or device that guides waves, such as electromagnetic energy.
[0055] The term "electromagnetic energy," as used herein, refers to
electromagnetic radiation (also "light" herein), which is a form of
energy exhibiting wave-like behavior. Electromagnetic radiation
includes radio waves, microwaves, infrared radiation, visible
light, ultraviolet radiation, X-rays and gamma rays.
Electromagnetic radiation includes photons, which is the quantum of
the electromagnetic interaction and the basic of light.
[0056] The term "adjacent," as used herein, includes next to or
adjoining, such as in contact with, or in proximity to. A layer,
device or structure adjacent another layer, device or structure is
next to or adjoining the other layer, device or structure. In an
example, a first structure that is adjacent a second structure is
directly next to the second structure. Adjacent components of any
device described herein are in such contact or proximity to each
other such that the device functions, such as for a use described
herein. In some instances, adjacent components that are in
proximity to each other are within 20 microns of each other, within
10 microns of each other, within 5 microns of each other, within 1
micron of each other, within 500 nm of each other, within 400 nm of
each other, within 300 nm of each other, within 250 nm of each
other, within 200 nm of each other, within 150 nm of each other,
within 100 nm of each other, within 90 nm of each other, within 80
nm of each other, within 75 nm of each other, within 70 nm of each
other, within 60 nm of each other, within 50 nm of each other,
within 40 nm of each other, within 30 nm of each other, within 25
nm of each other, within 20 nm of each other, within 15 nm of each
other, within 10 nm of each other, within 5 nm of each other, or
the like. In some instances, adjacent components that are in
proximity to each other are separated by vacuum, air, gas, fluid,
or a solid material (e.g., substrate, conductor, semiconductor, or
the like).
[0057] The term "field enhancement region," as used herein, refer
so a structure or device that enhances or focuses an electric field
in a waveguide or structure in optical communication with the
waveguide.
[0058] The term "electrode," as used herein, refers to a conductor
through which electrons enter or leave a device or structure. In
some cases, an electrode includes an anode of a device. In other
cases, an electrode includes a cathode of a device.
Field Enhancing Energy Collection Devices
[0059] In an aspect of the invention, field-enhancing energy
collection devices are provided. In an embodiment, a
field-enhancing energy collection device comprises a substrate. The
substrate comprises a base surface having at least one recessed
structure having one or more angled wall surfaces that taper
downward and away from the base surface, between which angled wall
surfaces is formed a recess void. The recess void is empty or
filled with a transparent or translucent material. The one or more
angled wall surfaces come in contact with, or in close proximity
to, the base surface. The one or more angled surfaces comprises an
electromagnetic energy conducting waveguide material, the
electromagnetic energy conducting waveguide material being
optically exposed to the recess void. The device further includes
an electrode adjacent the substrate. In some cases, the
electromagnetic energy conducting waveguide material includes a
cathode of the device and the electrode includes an anode.
Alternatively, the electromagnetic energy conducting waveguide
material includes the anode and the electrode includes the cathode.
The device comprises a distance ("gap") between the anode and the
electromagnetic energy conducting waveguide material of the
recessed structure. In some situations, the distance for the gap is
below about 100 nanometers ("nm"), with optimal distances depending
on material morphology. In an embodiment, for smooth surfaces the
distances are between about 1 nm and 60 nm, or 5 nm and 30 nm. In
certain embodiments, the distance ("gap") is about 1 nm to about
500 nm, about 1 nm to about 200 nm, about 1 nm to about 100 nm,
about 1 nm to about 50 nm, about 1 nm to about 20 nm, about 20 nm
to about 100 nm, about 20 nm to about 50 nm, less than about 20 nm,
less than about 50 nm, or any suitable distance. In some instances
where the electrons emit from the waveguide material to the anode,
the distance ("gap") is about 1 nm to about 500 nm, about 1 nm to
about 200 nm, about 1 nm to about 100 nm, about 1 nm to about 50
nm, about 20 nm to about 100 nm, about 20 nm to about 50 nm, less
than about 50 nm, or any suitable distance. In some instances where
the electrons tunnel from the waveguide material to the anode, the
distance is about 1 nm to about 50 nm, about 1 nm to about 20 nm,
less than about 20 nm, or any suitable distance.
[0060] FIG. 9 shows a functional block diagram of optical antennas
provided herein, in accordance with an embodiment of the invention.
The diagram shows three fundamental building blocks for a far-field
to near-field light trapping by geometrical waveguides. An optional
excitation of surface plasmon occurs depending on the resonating
frequencies of the selected metal and dielectric substrates. The
field concentration region leading to a gap located in the vicinity
of the ground plane is responsible of aggregating resonating fields
in order to free electrons to the ground plane surface. Electrons
are also freed (or generated) via quantum mechanical tunneling
(also "quantum tunneling" herein) by selecting the material and/or
configuration of metal-insulator-metal ("MIM") layers along the
inner layers of the geometrical waveguides and/or above the ground
plane. The functionalities of these building blocks and their
corresponding inter-connections are fundamentally different from
conventional near-field or photovoltaic effects. Furthermore, in
some cases such nano-structure optical antennas are fabricated as
arrays on rigid or flexible sheets or substrates to allow
additional flexibility with integration. In an example, flexible
sheets conform to a given geometrical shape, such as the one
depicted in FIG. 10, to allow electromagnetic near-field
manipulation via conformal mapping or sensing the directionality of
incident light. For example, in FIG. 10, incident electromagnetic
energy ("light") propagating along a vector parallel to the y-axis
is more effectively captured by nano-structures located along the
negative y-axis. In some cases, such nanostructures more
effectively sense the directionality of incident signal. In some
applications, this enables the mapping or sensing of the
directionality of incident light. That is, waveguides oriented
along the y-axis generate more electrons per unit time (or
"current") than waveguides oriented along the x-axis, which does
not appreciably (or detectably) generate any electrons in response
to light oriented along the y-axis. By determining which waveguides
or groups of waveguides generate the most current, the
directionality of incident light is determined.
[0061] In some embodiments, the gap between the electrode and the
electromagnetic energy conducting waveguide material of the
field-enhancing energy collection device comprises a vacuum void,
substrate, or a combination thereof. In some embodiments, the
electromagnetic energy conducting waveguide material is the
cathode. In other embodiments, the cathode is separate from the
electromagnetic energy conducting waveguide material. In certain
embodiments, the electromagnetic energy conducting waveguide
material and/or cathode comprises or is comprised of a conducting
material, such as one more materials selected from the group
consisting of Al, Ag, Au, Cu, Ni, Pt, Mn, Mg, W, Ti, Ru, Rh, C or
Graphene.
[0062] In some embodiments, the substrate of the field-enhancing
energy collection device is a non-conducting or semiconducting
material. The substrate comprises a dielectric, plastic, ceramic, a
semiconductor, or combinations thereof.
[0063] In some embodiments, the base surface dimensions 310 (e.g.,
the width, diameter, length, or the like of the recessed structure
at the base surface of a system or device described herein--see 310
in FIG. 3A) of the recessed structure is any suitable size. In
certain embodiments, a base surface dimension which is defined as
the opening on surface 303 of FIG. 3A, were the dimension is a
cross sectional dimension (e.g., diameter if the opening is
circular), or an edge dimension (e.g., the length of a side for
polygonal opening, or the circumference of a circular opening), or
the like. In some embodiments, the base surface dimension (such as
a cross sectional surface, e.g., diameter for a circle, or an edge
dimension) is greater than about 5 nm, greater than about 20 nm, or
greater than about 100 nm, or greater than about 250 nm, or greater
than about 500 nm, or greater than about 1 micrometer ("micron"),
or greater than 2 micrometers, or about 5 nm to about 5 microns
(e.g., for visible), or about 5 nm to about 20 microns (e.g., for
visible and infrared), or about 5 microns to about 20 microns, or
about 10 microns to about 20 microns (e.g., for infrared), or the
like
[0064] In some embodiments, the substrate of the field-enhancing
energy collection device is in contact with both the
electromagnetic energy conducting waveguide material and the anode.
In certain embodiments, the recessed structure is conical,
pyramidal, polygonal, a linear track, or a circular track.
[0065] In some embodiments, the recess void comprises a vacuum or
inert material. In certain embodiments, the inert material is an
inert gas or inert solid.
[0066] In other embodiments, the recess void comprises a
semiconducting photovoltaic ("PV") material, such as an organic PV
material. In certain embodiments, the organic photovoltaic material
comprises TiO.sub.2 and an electrolyte.
[0067] In some embodiments, the field-enhancing energy collection
device further comprises a transparent overcoat protection
layer.
[0068] In some embodiments, the electromagnetic energy conducting
waveguide material of the field-enhancing energy collection device
is situated on a surface of the recessed structure. The
field-enhancing energy collection device comprises a plurality of
recessed structures.
[0069] In some situations, the electromagnetic energy conducting
waveguide material of the plurality of recessed structures are
interconnected by electromagnetic energy conducting waveguide
material on a surface of the substrate opposite the base surface.
In certain embodiments, each of the plurality of recessed
structures includes an isolated anode that is spaced apart from the
recessed structure. In an embodiment, the isolated anode is spaced
apart from the recessed structure with the aid of a gap. The gap
electrically isolates the anode from the plurality of recessed
structures. In some cases this enables the device to act as an
image generating sensor.
[0070] In some embodiments, the anode comprises a flat surface
spaced apart from the electromagnetic energy conducting waveguide
material.
[0071] In certain embodiments, the anode comprises a flat surface
spaced apart from the electromagnetic energy conducting waveguide
material and further comprises a protrusion from the flat surface,
wherein the gap between the anode protrusion and the
electromagnetic energy conducting waveguide material is less than
the gap between the anode flat surface and the electromagnetic
energy conducting waveguide material.
[0072] Exemplary FIG. 1 is a perspective view of a tapered
waveguide collecting structure 100 of a certain embodiment of the
systems and methods described herein. The collecting structure
comprises a conducting material that tapers from a base 102 to a
point 104. In some embodiments, the conducting material is a thin
conducting film. In some situations, the conducting material
comprises metals or metallic materials, such as gold, copper,
silver, aluminum, graphene (a honeycomb crystal lattice of densely
packed carbon atoms in a one-atom-thick planar sheet), or other
carbon materials that are electrically conducting. In some
embodiments, the conducting material is comprised of one or more
conducting materials. In certain instances, the thickness of the
conducting material is on the order of the wavelength of
electromagnetic skin depth in the conducting medium.
[0073] As illustrated in FIG. 1, in one embodiment, the tapered
collecting structure 100 is inverted such that the base 102 is
located at the top and the point 104 is located at the bottom. The
cone is "open" at the top such that the base 102 is transparent to
electromagnetic radiation (e.g., visible and/or infrared light). In
some embodiments, the cone is filled with an optically transparent
material (e.g., transparent to visible and/or infrared light). In
suitable instances, the base is directed toward the sun or other
source of light or electromagnetic energy such that light (or
energy at another wavelength of the electromagnetic spectrum)
enters the waveguide via the top and propagates toward the tip
emitter. In some embodiments, the base of the illustrated
embodiment is circular. Other embodiments provide non-circular
bases to create node points within the cone. Unlike typical
waveguides, a common feature of the disclosed waveguides in some
instances is that the waveguide tapers to a point or opening with a
circular or polygonal shape. In other configurations having a
non-circular cross section, the waveguide in certain instances
tapers to a line.
Conical Waveuides
[0074] Exemplary FIG. 2 illustrates a perspective view of an array
110 of waveguides 100 according to certain embodiments of the
invention. FIGS. 3A and 3B illustrate a cross-sectional elevational
view of the array of waveguides of FIG. 2. As discussed below, each
or one or more waveguide in some instances functions as a cathode
(alternatively, a cathode is additionally included in a device
described herein). As shown in FIG. 3B, the tip 104 of the
waveguide is spaced apart from a conductive (or conducting) ground
plane 120 by a gap (or standoff layer) 122. The gap 122 is defined
by the tip 104 and a top surface of the conductive ground plane
120. In some embodiments, this region comprises the same material
as region 126 (see FIG. 3B). In certain instances, the conducting
ground plane comprises an electrical conductor and functions as an
anode. In one embodiment of FIG. 3, an electron emission region 124
is positioned between each waveguide (e.g., also serving as a
cathode) and the anode. In some embodiments, the waveguides are
formed in a dielectric substrate 126 that includes the standoff
layer 122 or into which the standoff layer 122 is formed.
[0075] The electromagnetic waves in suitable instances are incident
from above the broad open end (base) of each individual conical
waveguide 100. Each incident electromagnetic wave 130 creates a
mirror electric field in the waveguide comprising the electrically
conducting material. In suitable instances, light is reflected or
guided inward via plasmon waves created at the interface of metal
until the dimension of the tapered cross section (e.g., the
diameter for a cone having a circular base) equals the wavelength
of the electromagnetic wave. In some instances, the matching
dimensions create a standing wave that partially traps a wave 132,
as shown in FIG. 3B. Further, the electric field generated in the
conductive waveguide by the wave in suitable instances is combined
with the electric fields created by electromagnetic energy at other
wavelengths to create a high field region at the point 104 at the
tip of the waveguide. In some embodiments, the entire waveguide
structure functions as a cathode or electron emitter. With
sufficient localized field strength at the waveguide tip, the
electrons in suitable instances overcome the work function of the
metal to jump across the gap 124 to the ground plane (anode)
120.
[0076] In some embodiments, to optimize matching between trapping
light and electron emission and to prevent electron return from the
anode 120 to cathode point 104, a gap 124 that is under vacuum,
filled with an inert gas, or layered with MIM, metamaterial
structures, or other geometrical metallization that further enhance
gap capacitance and matching conditions, is used between the
cathode tip and the anode. In certain instances, the material
comprising the gap is chosen based on the field strength, which is
a function of the geometry and the intensity of the incident
electromagnetic wave. For instance, the gap is filled with a gas,
such as an inert gas. In some embodiments, the gas is the cause of
additional electron production which further enhance the current
generated and lower the electron emission energies. In some
instances, this also has the effect of changing the standoff
voltage across the cathode anode gap.
[0077] In some embodiments, as illustrated by the embodiment of
FIG. 3B, an electrically insulating (or dielectric) standoff 122 is
used to support the required distance between the tip 104 of the
cathode 100 and the anode 120. In some instances, the choice of
materials for the dielectric standoff is determined at least in
part by one or both of the dielectric field strength and the
manufacturing cost. In some embodiments, silicon oxides, plastic
and/or ceramics are used as the dielectric standoff 122. In other
embodiments, the distance between the cathode tip 104 and the anode
(ground plane) 120 is less than about 100 nanometers ("nm"), or 90
nm, or 80 nm, or 70 nm, or 60 nm, or 50 nm, or 40 nm, or 30 nm, or
20 nm, or 10 nm, depending on the optical energy collecting
application.
[0078] Without wishing to be bound by theory, FIG. 4 illustrates
the enhanced field at the tip 104 of the waveguide 100. In FIG. 4,
the tip of the waveguide is pointing upward for convenience in
presenting the graph. The units in FIG. 4 are normalized with
respect to a maximum field at the location of the tip positioned at
relative coordinates (0, 0). When free electrons in the
electrically conducting material in the cathode or waveguide 100
interact with the electric field of the electromagnetic wave, in
suitable instances the free electrons oscillate at the frequency of
the electromagnetic wave, as long as the plasma frequency for the
metal is above the electromagnetic wave frequency. In some cases,
such resonance phenomenon gives rise to field enhancement at the
tip. In some embodiments, the resonance is not through plasmonic
coupling but through the geometry of the optical antenna. In such a
case the resonance is a function of the varying size of the antenna
horn itself, creating a field compression region at the tip.
[0079] Exemplary FIGS. 5A and 5B illustrate detailed cross-sections
of a conical waveguide collector 200 having an upper base 202 and a
lower tip (cone point) 204, in accordance with some embodiments of
the invention. In some instances, the tip 204 is spaced apart from
a ground layer (anode) 220 by a gap 222 as shown in FIG. 5A. In
some instances the tip is an opening with a circular or polygonal
shape as shown in FIG. 5B (204). In some embodiments, the wall
forming the waveguide collector comprises a dielectric 230 metal
layer 232. The electric field in some instances propagates to the
cone point 204. Plasmon surface waves create a coupling of the
light wave to the metal surface wave, thereby creating a waveguide.
The plasmon wave is dependent on various factors, such as
frequency, material and thickness. Plasmons are discussed in detail
in, for example, S. Maier, Plasmonics: Fundamentals and
Applications. Springer. (ISBN 978-0387331508) (2007); H. Atwater,
"The Promise of Plasmonics", Scientific American 296 (4): 56-63
(2007); and Dione, Sweatlock, Atwater and Polman, Plasmon slot
Waveguides: Towards chip-scale propagation with subwavelength-scale
localization, Physical Review B 73, 035407 (2006), which are
entirely incorporated herein by reference.
[0080] In some instances, surface plasmons couple the
electromagnetic field energy of the incident light wave to the
conductive region and propagate energy along the interface of
conducting region 232 of the waveguide and either insulating 230,
dielectric 230, gas (202) or vacuum region 202. In an embodiment,
the region 230 is translucent to the wavelength of light to be
collected. In some instances, the region 230 is also used to
preferentially absorb certain wavelengths of light to either
filtering the light or creating regions for downshifting the light,
as with photolumiscence materials. In some embodiments, a plasmon
surface wave is enhanced or modified by placing a thin dielectric
layer or a different conducting material (e.g., metal,
semiconductor, graphene) over the metal layer. Surface plasmon
waves that traverse a dielectric and conducting interface in some
instances are controlled by features on the surface, as shown in
Pendry, Martin-Moreno, Garcia-Vidal, Mimicking Surface Plasmons
with Structured Surfaces, Science 305, 847 (2004); DOI:
10.1126/science.1098999, which is entirely incorporated herein by
reference. In some embodiments, light trapping and electron
emission are further enhanced by incorporating slanted or
cylindrical surfaces at the top or bottom portion of the tapered
structure, or by including grooves or some sort of surface
roughness along the inner surface of the sloping geometry, or by
including metamaterial resonating structures or MIM layer along the
inner side.
[0081] In some embodiments, such as FIG. 5A, the anode 220 is a
flat plane across from the cathode tip(s) 204; in other
embodiments, such as FIG. 5B, the anode 234 includes an inverted
conducting tip 233 to further enhance the electric field generated
upon propagation of light in the collector 200. In general, there
is a gap 235 to provide an electrical standoff between the cathode
204 and anode 234. In some embodiments, the gap 235 is, is made up
of, or comprises a vacuum, filled with a gas (e.g., an inert gas)
or other material (e.g., substrate material as described herein).
In certain embodiments, a vacuum is used when the design requires
no interaction of material with the electron as it transports
across the gap 222. However a gas in suitable instances is used to
interact with the electrons to either slow the electrons or too
transfer energy from the electrons and create more electrons but
with lower energies. In certain instances, the material in the gap
affects the field strength, allowing a tailoring of the emission
for specific incident light intensities and energies and therefore
tailoring the final electron emission to the environment.
[0082] In some embodiments of the tapered structure has more than
one taper shape, such as shown in FIGS. 11A, 11B, and 11C. In some
instances, the taper proximal to the base surface of the device has
a first angle and distal to the base surface (or at or proximal to
the tip) of the device has a second angle or other shape (e.g., a
convex, concave, rounded, or the like shape), such as orthogonal to
the base surface. In some instances, the tip of the tapered
structure includes a sharper tapered region with a gap toward the
bottom as illustrated in FIG. 11C, e.g., to further increase field
intensity, and hence electron emission. The tapered structures
illustrated in FIG. 11 are separated from the ground plane 220 with
the gap 222, as illustrated in FIG. 5B. The ground plane includes a
top MIM layer, e.g., to further enhance electron emission. In some
embodiments, the gap 235 includes a vacuum, filled with a gas
(e.g., an inert gas) or other material (e.g., substrate material,
as described herein). In certain embodiments, a vacuum is used when
the design requires no interaction of material with the electron as
it transports across the gap 222. However, a gas in suitable
instances is used to interact with the electrons to either slow the
electrons or too transfer energy from the electrons and create more
electrons but with lower energies. In certain instances, the
material in the gap also affects the field strength, allowing one
to tailor the emission for specific incident light intensities and
energies and therefore tailor the final electron emission to the
environment.
[0083] In some embodiments, gaps between anodes and cathodes is
under vacuum at a pressure less than about 760 torr, or 1 ton, or
1.times.10.sup.-3 ton, or 1.times.10.sup.-4 ton, or
1.times.10.sup.-5 torr, or 1.times.10.sup.-6 ton, or
1.times.10.sup.-7 ton, or 1.times.10.sup.-8 ton, or
1.times.10.sup.-9 torr. In some cases, the walls of the anode and
cathode defining the gap are hermetically sealed to provide a
vacuum at a desirable pressure. The pressure is selectable so as to
effect a desired emission in the region between the cathode and
anode.
[0084] By way of non-limiting exemplary FIG. 1, varying
cross-sectional diameter of a certain embodiment of the conical
waveguide 100 (or distance across a cross section for other shapes)
is preferably to be on the order of the wavelength of the
electromagnetic radiation being collected. Varying the distance
from the conical waveguide top surface to the bottom tip may
improve matching conditions and electron emission. For collecting
visible light, the inner diameter of the cone in some embodiments
varies between approximately 800 nanometers to under 400
nanometers. In some cases, the diameter is also increased or
decreased based on harmonics of the wave with the harmonic
dimension described by n.lamda./2, where `n` is an integer and
`.lamda.` is the wavelength of the electromagnetic wave. In one
embodiment, the diameter is a multiple of wavelengths for other
applications. In certain embodiments, the inner diameter closest to
the point is sufficiently small so the cone is able to collect
electromagnetic energy in the ultraviolet range.
[0085] In certain embodiments, the waveguide comprises an
electrically conducting metallic medium that has a plasma frequency
above the desired collecting frequency of light. The plasma
frequency, .omega..sub.pe (in radians per second), is defined
as:
.omega. pe = ( n e e 2 o m e ) 1 / 2 rad / s ##EQU00001##
where `n.sub.e` is the electron density, `e` is the electric
charge, `.di-elect cons..sub.o` is the permittivity of free space
and `m.sub.e` is the mass of an electron. The frequency is then
fp=.omega..sub.pe/2.pi..
[0086] In some embodiments, metals, such as, for example, gold,
silver, aluminum, platinum, or composite metals, are used for
visible light collectors. In certain instances, some metals, such
as copper, have a plasma frequency in the visible range, yielding a
distinct yellow color. In some situations, such metals are less
favorable materials for full spectrum applications because they
exclude collection of some of the electromagnetic spectrum. In
other situations, such metals are preferable candidates for
applications in which light of higher frequency is to be filtered
out. In such applications, the disclosed system filters light of a
particular or predetermined frequency. The plasma frequency of
metals and material are known by those in the art and are chosen
depending on the spectrum of electromagnetic radiation that is to
be collected.
[0087] The thickness of the metal is also important to consider;
insufficient amount of metal may generate a significant amount of
transmission of the electromagnetic energy into the substrate. Also
the smoothness of the metal is also important, especially between
the metal and the recess void. The optical properties of the metal
may change if the metal surface is too rough or corrugated.
Likewise, if the metal is thin and on the order of the optical
frequency skin depth or less, the roughness of the metal substrate
interface may also affect the response of the waveguide.
[0088] In addition, disclosed herein is electron emission off of an
array of structures similar that shown in FIG. 5A or 5B.
[0089] In suitable instances, when the field is sufficient or the
localized electron density is sufficient, electrons are emitted
from the tip 104 of the cathode (waveguide) 100 to the anode
(ground plane) 120 in the embodiment of FIGS. 1-3. In some
embodiments, the field is modified by placing a high-resistance
voltage source 242 of FIG. 6 in parallel with the cathode to anode
path. In other embodiments, as shown in FIG. 6, a voltage source
240 comprises a direct current (DC) source (e.g., battery, or an
inherent voltage from dissimilar metals or a semiconductor bandgap)
242. In some situations, a diode 244 is added to restrict the
backflow of electrons from the anode to the cathode. The voltage
source is positioned in parallel with the cathode-to-anode path
between a top conducting plane 246 and the anode. In some
embodiments, this voltage source is also an alternating current
(AC) source to create a coupling current to an external (or
outside) load. In some embodiments, the top conducting plane
interconnects the plurality of waveguides 100 (FIG. 2). By way of a
non-limiting example, a load 248 is connected between the top
conducting plane and the anode (ground plane). In an example, the
load is any device that uses electrical energy (or power) generated
by devices and structures provided herein. The embodiment
illustrated in FIG. 6 is particularly useful when the waveguides
are used in low intensity environments, such as in sensor
applications. In an alternative embodiment (not shown), two or more
waveguides are placed in series to increase the generated
voltage.
[0090] In some embodiments, the plurality of conical waveguides
100, such as those shown in FIGS. 2 and 3, are tightly packed to
occupy as much of the surface area as possible in order to maximize
the collection area. In other applications the spacing between the
waveguides is used to create surface plasmon waves that are
dependent on the distances between the waveguides, adding an
additional resonant mode. The current produced by the multiple
waveguides is a function of the light intensity, the geometries and
metals used in the waveguides, the energy associated with the
spectrum and the overall resistance. In some embodiments, the
multiple waveguides are manufactured using simple materials that
embed the tapered geometry in a double metal dielectric layer
similar to Mylar sheets. In certain embodiments, the thickness of
the entire device is less than four micron, or less than 1000
nanometers ("nm"), or less than 500 nm, or less than 100 nm. In
other embodiments, a thicker anode is used to provide structural
support, increasing the overall thickness to over 4 microns. As
discussed above, in certain embodiments, a vacuum or gas is
embedded in the emission region 124 between the tips 104 and the
ground plane 120. In other embodiments, other insulating materials
are also used. In some embodiments, the distance between the tips
and the ground plane is maintained (and the tips and ground plane
are electrically insulated) with the aid of insulating standoffs
122. The embedded gas or vacuum in the emission region 124 allows
for tailoring the electron emission energy and the number of
electrons produce based on the intensity and energy of the incident
electromagnetic waves.
Tube Waveguide
[0091] In some embodiments, exemplary FIG. 7 shows an alternative
version for specific wavelength collection. The waveguide is a tube
(.THETA. is 90 degree), with conducting material 100, cathode
emitter 204 and anode plane 120. The structure is supported in one
embodiment by insulating material 126 and the inside of the cones
are filled with transparent material 230 chosen for translucence
and the effect on electron emission and the effect on the field
strength between the cathode and anode. In another embodiment, this
option is also modified by an inverted anode structure (not shown)
but similar to 233 in FIG. 5B.
[0092] Exemplary FIG. 8 shows another embodiment of the invention
where the tapered structures are in a track configuration. In some
embodiments, these structures are concentric circles or in
spiraling shapes. In this configuration the cathode emitter 204 is
a continuous surface above the anode 120. The material in the gap
region 235 is similar to that described in the other embodiments of
the device. In some embodiments, this configuration has advantages
for manufacturing specific regions that are isolated from other
collection regions and create additional resonant frequencies that
are collected based on the distance between the track regions
through surface plasmons.
Light Collection and Enhancement Structures
[0093] In another aspect of the invention, a field-enhancing energy
collection device includes one or more field enhancement regions
(or structures), which are configured to provide electric or
magnetic field enhancement to the field-enhancing energy collection
device (or antenna). Field enhancement regions are applicable with
various field-enhancing energy collection devices provided
herein.
[0094] Field enhancement regions provided herein include one or
more field enhancement structures. In some cases, field enhancement
structures include one or more structures with sharp points, such
that the electric field at one or more tips of the one or more
structures diverges (or approaches divergence) (see, e.g., FIG.
11C). In some cases, such as FIG. 5B, the anode has a pointed
electrically conducting structure 233 pointing toward the cathode
to further enhance the field. In other cases, a field enhancement
structure includes a quantum mechanically tunneling ("tunneling")
junction, such as that shown in FIG. 12B using a thin insulator or
oxide 5.
[0095] An individual waveguide in an array of waveguides includes a
field enhancement region. Alternatively, an array of waveguides
includes a field enhancement region.
[0096] In an embodiment, field enhancement regions are disposed
adjacent an electrode (e.g., anode) of a field-enhancing energy
collection device and a waveguide (e.g., cathode) of the device. In
another embodiment, field enhancement regions are in contact with
an electrode of the device.
[0097] FIG. 12A shows an optical waveguide, in accordance with an
embodiment of the invention. FIG. 12B shows a device for providing
an alternative mode of rectification from FIG. 12A, in accordance
with an embodiment of the invention.
[0098] With reference to FIG. 12A, the optical waveguide includes
an optically transparent top surface 1, a light collection layer 2,
support structure 3, hollow tapered body 4, electrical insulator 5,
a gas or vacuum region 6, an electrical return plane 7, and an
emission region 8. The electrical return plane 7 is referred to as
a collector or electrode, in some cases. In some situations, the
collector 7 is an anode and the top surface 1 is a cathode. In an
embodiment, the top surface 1 and collector 7 are electrodes.
[0099] In some embodiments, the structure of FIG. 12B enhances the
potential field absorption by allowing light to enter on both sides
of the light collection and enhancement structure 2. Light enters
the optical waveguide through the top of the structure, as
indicated. In an embodiment, the supporting structure 3 is formed
of an optically transparent material.
[0100] In some cases, the device of FIG. 12A includes an
electrically conductive material covering the support structure 3,
which enables electrical current to flow to the waveguide 2. In an
embodiment, this material is optically transparent, allowing light
to enter both sides of the recessed structure. In one example,
material indium tin oxide (ITO) is used as the electrically
conductive material covering the support structure 3. In another
example, other electrical conductors that are transparent to the
desired collection wavelengths are used. In an embodiment, the
light collection and enhancement structure 2 is a tapered structure
formed of a metal (e.g., one or more of Ag, Al and Au), graphene,
or other electrically conductive material having a plasma frequency
to enable electrons in the material to respond to light frequencies
to be collected in the structure. The light collection and
enhancement structure 2 is supported by the support structure 3. In
some situations the support structure 3 is optically
transparent.
[0101] In FIG. 12A, electron emission is used for rectification. In
some embodiment, the electrical insulator 5 has a thickness between
about 1 nanometer ("nm") and 40 nm, or 10 nm and 300 nm, or 20 nm
and 100 nm. The emission region 8 is formed of a sharp or
substantially sharp tip, the sharp tip creating higher field to
enhance electron emission. In some situations, the enhanced field
at the emission region 8 causes electrons to overcome the work
function and traverse the gas or vacuum region 6. The electrons are
then be collected by the electrical return plane 7, which is formed
of an electrically conductive material. In FIG. 12A, light enters
both into the open collector region 4 and through the optically
transparent support structure 3 and is concentrated through
resonance, geometric compression and plasmonic waves to create
field enhancement at the emission region 8 due to the tapered
shape. In some situations, the hollow tapered body 4 has the shape
of a cone. Resonance occurs through wavelength scale geometries and
harmonics in the tapered region. This creates an enhanced field on
the inner surface with a high field region at the emission region
8. In some situations, light also enters through top surface 1 and
into the support structure 3. In some cases, the top surface 1 is
an electrical contact of the device of FIG. 12A. The top surface 1
is optically transparent but conducts electricity. Upon entering
the support structure 3 through the top surface 1, light is
concentrated on the outer metal surface 2. The support structure 3
is optically transparent to allow light into the structure. In an
embodiment, the thickness of the light collection and enhancement
surface (or structure) 2 is greater than the skin depth of the
desired light collection frequencies in the particular metal. For
example, the light collection and enhancement structure 2 has at
thickness between about 1 nm and 500 nm, or 5 nm and 100 nm. For
cases in which the light collection and enhancement structure 2 is
formed of Al, Ag or Au, the thickness of the light collection and
enhancement structure 2 is greater than about 5 nm, or 10 nm, or 40
nm, or 50 nm.
[0102] In an embodiment, the plane 7 is in electrical communication
with a load, which is in electrical communication with the top
surface 1. Upon exposure of the light collection and enhancement
structure 2 light, electrons are emitted from the emission region 8
and collected at the plane 7. Electrons subsequently travel to the
load and return to the top surface 1.
[0103] In some embodiments, the device of FIG. 12B employs a metal
insulator metal (MIM) structure for electron tunneling across an
insulating layer of the MIM structure. The MIM is defined by the
light collection layer 2, insulator 5 and collector 7. In the
device of FIG. 12B, electrons from field concentration point 8
tunnel across the insulator 5 to the collector 7. For this
configuration, the thickness of the insulator is substantially thin
to allow for electron tunneling across the insulator. In some
situations, the thickness of the insulator is calculated using
Simmons electron tunneling approach, in which case the insulator
has a thickness between about 1 nm and 30 nm. In other embodiments,
the MIM structure is combined with or modified by other quantum
mechanical tunneling diodes, such as those described in Cowell et
al., Adv. Mater. 2011, 23, 74-78) and Dagenais et al., "Solar
Spectrum Rectification Using Nano-Antennas and Tunneling Diodes",
Optoelectronic Integrated Circuits XII, Proceedings of SPIE Volume:
7605 (12 Feb. 2010), which are entirely incorporated herein by
reference
[0104] In some implementations, the insulator 5 includes an oxide,
such as a metal or insulating oxide. In an example, the insulator 5
is formed of titanium oxide (e.g., TiO.sub.2), aluminum oxide
(e.g., Al.sub.2O.sub.3), and/or silicon oxide (e.g., SiO.sub.2). In
some cases, the insulator is chosen for various properties that
include standoff voltage and the ability to manufacture and deposit
in a smooth fashion on anode 7.
[0105] In some embodiments, the insulator 5 is formed using atomic
layer deposition (ALD), plasma-enhanced ALD, chemical vapor
deposition (CVD), or plasma-enhanced CVD, to name a few examples.
In some embodiments, the insulator 5 has a substantially low defect
density, to minimize shorts between the light collection layer 2
and collector 7. In addition the insulator 5 has one or more
surfaces. In another configuration the electron return path 1 is
above the insulator 5, as shown in FIG. 12B. This configuration
permits the optically transparent support structure 3 to be
uncovered, eliminating the need for the electrical return material
1 to be transparent. In this case, the top surface of the optically
transparent support structure 3 does not have the conducting
material 1 on the top surface as in FIG. 12A, rather the cathode
conducting plane 1 sits over insulator 5. Having the cathode or
electron return layer 1 over the insulator has an additional
potential advantage in that electrical current is not conducted
through the light collection layer (or collecting material) 2. In
some cases, this reduces or eliminates potentially negative effects
from electromagnetic fields generated by current flowing on the
light collecting layer 2.
[0106] In some situations, waveguides and optical antennas provided
herein are combinable with, or modifiable by, other structures,
systems and/or methods, such as, for example, structures, systems
and/or methods described in U.S. patent application Ser. No.
12/259,104, filed on Oct. 27, 2008; U.S. Pat. No. 3,994,012 to
Warner, Jr. ("PHOTOVOLTAIC SEMI-CONDUCTOR DEVICES"); M. Laan, J.
Aarik, R. Josepson and V. Repan, Low current mode of negative
coronas: mechanism of electron emission, J. Phys. D: Appl. Phys.,
36, 2667-2672, 2003; V. Repan, M. Laan and T. Plank, Electric Field
Modeling for Point-Plane Gap, Institute of Experimental Physics and
Technology, University of Tartu, Tahe Estonia publication, 2002; P.
Dombi and P. Racz, Ultrafast monoenergetic electron source by
optical waveform control of surface plasmons, Optics Express, Vol.
16, No. 5, pages 2887-2893, 3 Mar. 2008; and Mark I. Stockman,
Matthias F. Kling, Ulf Kleineberg and Ferenc Krausz, Attosecond
nanoplasmonic-field microscope, Nature Photonics, Vol. 1, pages
539-544, Sep. 3, 2007; Palash Bharadwaj et al., Advances in Optics
and Photonics 1, 438-483 (2009); Peter Muhlschlegel, Ph. D. Thesis,
University of Basel/Germany, February 2006; and Jong-Yeon Park et
al., Japanese Journal of Applied Physics Vol. 43, No. 6A, 2004, pp.
3320-3327; Knight et al., "Photodetection with Active Optical
Antennas," Science 332, 702 (2011); and Kotter et al., "Solar
NANTENNA Electromagnetic Collectors", ASME Proceedings of the 2nd
International Conference on Energy Sustainability, Aug. 10-14,
2008, Jacksonville, Fla., USA, which are entirely incorporated
herein by reference.
[0107] Applications using visible light are broad and in some
embodiments include any application requiring electrical energy
where the system is exposed to light, such as, for example,
buildings, cars, electronics, and the like. Applications are not
limited to outdoor applications because the system may be
positioned anywhere sufficient light is available. In some
instances, the system is advantageously enhanced using light
focusing techniques including mirrors or Fresnel lenses. In
suitable instances, other applications include refueling aircraft
using infrared or microwave energy, with conical sizes on the order
of the intended wavelength of electromagnetic radiation. In some
embodiments, for lower frequency applications, the intensity is
increased to generate strong enough localized fields since the
energy per photon is lower at lower frequencies.
[0108] It should be understood from the foregoing that, while
particular implementations have been illustrated and described,
various modifications may be made thereto and are contemplated
herein. It is also not intended that the invention be limited by
the specific examples provided within the specification. While the
invention has been described with reference to the aforementioned
specification, the descriptions and illustrations of the preferable
embodiments herein are not meant to be construed in a limiting
sense. Furthermore, it shall be understood that all aspects of the
invention are not limited to the specific depictions,
configurations or relative proportions set forth herein which
depend upon a variety of conditions and variables. Various
modifications in form and detail of the embodiments of the
invention will be apparent to a person skilled in the art. It is
therefore contemplated that the invention shall also cover any such
modifications, variations and equivalents.
* * * * *